Bush told a NATO session that included Afghan President Hamid Karzai on Thursday that the United States is committed to winning the war in Afghanistan and will be even after he leaves office in January. His vow came as European allies agreed to supply nearly 2,500 more troops themselves to join 3,500 additional U.S. Marines sent by Bush.

"The president wanted to make it clear that the United States is committed to Afghanistan for the long haul and to send a signal to our allies that at the same time we are asking them to commit additional troops to Afghanistan that they know that we will also continue to have a significant troop presence . . . regardless of the situation in Iraq," said White House spokesman Gordon Johndroe.

The pledge comes as violence and insurgent activity is spiking in parts of Afghanistan. The administration's promise of more troops could indicate the beginnings of a push, similar to the buildup of forces in Iraq over the past year, to step up counterinsurgency operations next year. Such a decision would probably fall to Bush's successor, but Defense Secretary Robert M. Gates said he senses bipartisan support.

"I think that no matter who is elected president, they will want to be successful in Afghanistan," Gates told reporters traveling with him Friday as he left the summit for a Middle East trip.

National security adviser Stephen J. Hadley signaled the commitment to sending additional U.S. troops to Afghanistan in 2009 during a briefing in Bucharest late Thursday. "We have plans to contemplate additional contributions of troops in Afghanistan in the south in 2009," Hadley said, adding that "these are all in addition to" the 3,500 Marines now going to Afghanistan.

Neither Hadley nor Gates indicated how many troops.

Commanders in Afghanistan have said they could use as many as two to three additional brigades, or nearly 10,000 troops. Gates said he would like to wait until after the additional U.S. Marines in Afghanistan return home later this year to decide on 2009 troop levels, suggesting that more troops could be deployed "some number of months" after the Marines return.

Michael E. O'Hanlon of the Brookings Institution warned that adding forces to Afghanistan could hurt efforts in Iraq. "We shouldn't shortchange the Iraq mission to find the brigades for Afghanistan," O'Hanlon said.

Gen. David W. McKiernan, the nominee for commander of NATO's International Security Assistance Force in Afghanistan, told the Senate Armed Services Committee on Thursday that the United States should examine options for deploying more brigades. "There are certainly no signs that the insurgency is ready to collapse," McKiernan said. He emphasized that NATO needs to contribute more forces and remove combat limitations some member countries impose, "as they continue to degrade NATO capabilities."

Sen. John W. Warner (R-Va.) on Thursday expressed concern about the alliance. "I fear that if NATO does not enable this country to succeed in its goals, the commitment of the nations of the world to continue NATO will be tested," Warner said.

Hadley and other officials said they were pleased by the NATO allies' support at the summit but added that the United States did not get as many additional troops as commanders have been seeking.